Looking Up: Jupiter pairs up with Neptune

Friday

Jun 26, 2009 at 12:01 AMJun 26, 2009 at 1:21 PM

An unusual chance to see a close pairing of Jupiter and Neptune awaits the next clear night. Due to its magnificence, brilliant Jupiter is easy to pick out and probably most people have seen it without even knowing it. Neptune, however, although it is a giant planet as well, is so far away very few people have ever seen it. This is a chance to find Neptune with a pair of binoculars or a small telescope with little trouble, since it is close by the King of Planets, Jupiter.

Peter Becker

An unusual chance to see a close pairing of Jupiter and Neptune awaits the next clear night. Due to its magnificence, brilliant Jupiter is easy to pick out and probably most people have seen it without even knowing it. Neptune, however, although it is a giant planet as well, is so far away very few people have ever seen it. This is a chance to find Neptune with a pair of binoculars or a small telescope with little trouble, since it is close by the King of Planets, Jupiter.

Planets in their courses pass each other frequently, though it is rare to have them very close together. Please note that the paring is only a chance alignment. Contrary to ridiculous rumors and fortune-telling you might hear or read, the planets won’t and don’t affect life on Earth in the way that the rumors imply. Claims have been made in the past that planetary alignments would couple their gravitational pull and wreak havoc on the tides and minds of the innocent. Earthquakes have been foretold, as Earth’s crust supposedly can’t bear the attention of its planetary cousins. Fear not. There are plenty of “signs of the times,” but this is not one of them. Also consider the fact that Earth likewise makes chance alignments with other planets, say Venus and Mercury, and as far as we have heard, Mars is still OK.

The truth of the matter is that the planets are so extremely far apart, even their combined gravitational pull does not affect us significantly.

One way these planetary pairings (also called conjunctions) do affect us is that they are another reason to look up and delight in the wonders of the universe, and offer a handy lesson in solar system dynamics and our place in the scheme of things.

As of June 24, Jupiter may be seen rising in the southeast at 11:19 p.m. EDT -- assuming you have a flat horizon. Situated in the constellation Capricornus, it is not relatively high in the south until 4:32 a.m. (when it transits the Meridian- the imaginary south-north line on the sky, which extends overhead). In another week, on July 1, Jupiter rises at 10:51 p.m. and transits at 4:03 a.m.

Just over a half-degree north of Jupiter is the planet Neptune. Remember, the apparent width of the full moon is about one-half degree.

One degree on the sky is broken down into 60 “minutes of arc” noted as a single apostrophe (’). Each minute of arc is broken down into 60 seconds of arc (”). On July 9, Neptune is closest, only 34’ from Jupiter. On July 13, they are 37’ apart. Remarkably, between these dates, you willl see a fifth-magnitude star right between these planets, known as Mu Capricorni.

As another reminder, astronomers rate the apparent brightness of a star or planet (or other sky object) by the magnitude scale. The brightest stars we see at night are magnitude 0 or brighter, which then have a negative number (the brightest, Sirius, is magnitude -1.44). Most of the Big Dipper stars are approximately magnitude +2. The faintest stars most people can see under a dark sky, without optical aid, is +6. Jupiter is currently shining at -2.8, brighter than any star in the night sky. Neptune is +7.8 and requires binoculars to pick it out like a dim star.

If you use even a small telescope, Jupiter will easily show its disc, currently about 49” across. Its four bright attendant moons will be nearby. Neptune is only 2.3” across, and to see it as more than a “star” requires a telescope of about 4-inch aperture and around 150x magnification, as well as a night of steady air (good “seeing”).

The conjunction of these planets and the star is purely a matter of perspective. Jupiter, at its closet to Earth, is about 370 million miles away. Neptune is a lot farther - 2.8 BILLION miles from Earth at its closest, which is the main reason it is so much fainter. Both shine at us with reflected sunlight, by the way. Mu Capricorni, like other stars, glow with their own tremendous light. This star is approximately 90.2 LIGHT YEARS distant (around 523 TRILLION miles). Yet we still see it! Imagine the power put out by a star!

Saturn is visible low in the west as evening twilight fades. If you are up before dawn, look for brilliant Venus low in the east, with dimmer, reddish Mars about 4 degrees to the upper right. Venus, which is close to the sun and reflects a lot of sunshine with its white clouds, shines at a dazzling -4.1.

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